1. Field of the Invention
The present invention relates to endoscopic systems, and more particularly to a structure for use in a medical field and forming and displaying a spectral (video) image in an arbitrarily-selected wavelength band of image information.
2. Description of the Related Art
In the electronic endoscopes using solid-state imagers, attentions are recently drawn to the spectral imaging combined with a narrow-band pass filter depending upon the spectral reflectance upon the digestive organ (the gastric mucous membrane, etc.), i.e. narrow band imaging—NBI. The instrument is provided with three narrow-(wavelength) band-pass filters. By sequentially outputting illumination light through the narrow-band pass filters, three signals obtained from the illumination light is processed in a manner similar to those for R, G, B (RGB) signals while changing the weighting, thereby forming a spectral image. With such a spectral image, fine tissues, etc., not obtainable in the related art, can be extracted out of the digestive organ such as the large intestine.
Instead of the field-sequential type using a narrow-band pass filter, there is a proposal on forming a spectral image by an operation with an image signal obtained from white light in a simultaneous type arranging a fine-mosaic color filter for a solid-state imager, as disclosed in JP-A-2003-93336 and Yoichi Miyake “Analysis and Evaluation of Digital Color Images,” University of Tokyo Press, pp 47, 147-153. This includes to determine, as matrix data (coefficient set), a relationship between a digitized data of sensitivity characteristics of RGB colors and digitized data of a spectral characteristic of through a particular narrow band, and to artificially obtain a spectral-image signal through a narrow-band pass filter by operating the matrix data with the RGB signals. Where forming a spectral image by such an operation, there is no need to prepare a plurality of filters corresponding to a desired wavelength band and hence no need to exchange those. This can avoid the instrument from increasing in size and hence lower the cost.
However, there is a tendency toward the complicated circuit configuration even for the endoscope capable of producing a spectral image based on an operation as above. There is a further need to make the structure simple. Meanwhile, devising is essentially required to efficiently obtain information useful in diagnosis, etc. through effective utilization of a plurality of spatial images different in wavelength band.
Meanwhile, in the related-art endoscope, the color image taken of a subject is recorded (filed) in the image recorder/display unit. The spectral image as above can be recorded in the image recorder/display unit in order for later observation. However, with such a spectral image, because various fine tissues can be rendered by selecting the wavelength band thereof, there are cases that the spectral images to record is in a plurality or a multiplicity in the number. In such a case, reference information is necessarily recorded at the same time. Namely, by selecting a wavelength band, various fine tissues can be rendered including, say, a comparatively thick blood vessel, a capillary vessel, a blood vessel deep in position, a blood vessel shallow in position and a cancerous tissue. Meanwhile, it is possible to render, as a target, a difference between particular substances, e.g. a difference between oxy-hemoglobin and deoxy-hemoglobin. Moreover, in order to extract a particular fine tissue successfully, there is a need of regulating a wavelength band to select. For forming and observing such a spectral image, its wavelength band constitutes vital information.
Meanwhile, the spectral image is generated based on the usual color image as an original image. When observing a spectral image, if comparison can be done with its basic color image, the subject can be easily observed/diagnosed thus obtaining an instrument easier to handle. Furthermore, where there are a plurality or multiplicity of spectral images to record, efficient recording operation, etc. are desired.